Nickel(II)-Nickel(II) Azadithiolates: Synthesis, Structural Characterization, and Electrocatalytic H2Production

Article abstract of DOI:10.1021/acs.organomet.0c00130

Azadithiolato-bridged dinuclear Ni2 complexes with the general formula [(η5-C5H5)Ni{(μ-SCH2)2NC6H4R-4}Ni(diphos)]BF4 (8-11, R = H, Cl, MeO; diphos = dppv, dppe) have been prepared by a well-designed synthetic method including the following three separate

Full text of DOI:10.1021/acs.organomet.0c00130

pubs.acs.org/Organometallics
Article
Nickel(II)−Nickel(II) Azadithiolates: Synthesis, Structural
Characterization, and Electrocatalytic H2 Production
Li-Cheng Song,* Wen-Bo Liu, and Bei-Bei Liu
Cite This: https://dx.doi.org/10.1021/acs.organomet.0c00130
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Azadithiolato-bridged dinuclear Ni2 complexes with the general
formula [(η5-C5H5)Ni{(μ-SCH2)2NC6H4R-4}Ni(diphos)]BF4 (8−11, R = H,
Cl, MeO; diphos = dppv, dppe) have been prepared by a well-designed synthetic
method including the following three separate reaction steps. The first reaction
step involves preparation of the bis(thioester) precursors 4-RC6H4N(CH2S-
(O)CMe)2 (1−3, R = H, Cl, MeO) by a cocondensation reaction of aniline or
its substituted derivatives 4-RC6H4NH2 with 37% aqueous formaldehyde and
thioacetic acid. The second step involves preparation of the mononuclear Ni
precursors (diphos)Ni[(SCH2)2NC6H4R-4] (4−7, R = H, Cl, MeO; diphos =
dppv, dppe) by a one-pot reaction of bis(thioester) precursors 1−3 with t-
BuONa followed by treatment of the resulting disodium intermediates 4-
RC6H4N(CH2SNa)2 with (dppv)NiCl2 and (dppe)NiCl2, respectively. The third
step involves preparation of the targeted dinuclear Ni2 complexes 8−11 by
coordination reactions of mononuclear Ni precursors 4−7 with [η5-C5H5Ni]+
generated in situ from dissociation of the triple-decker sandwich complex [(C5H5)3Ni2]BF4. While all of the prepared compounds
1−11 have been characterized by elemental analysis and various spectroscopic techniques, the molecular structures of precursor
complex 5 and targeted complexes 9 and 11 have been further confirmed by X-ray crystallography. In addition, the two
representative targeted complexes 8 and 9 have been found to be catalysts for proton reduction to hydrogen using acetic acid as the
proton source under electrochemical conditions.
Inspired by the well-elucidated structure shown in Figure 1a,
synthetic chemists have prepared a large number of the hetero-
and homodinuclear Ni−M (M = Fe, Ru, Mn, Mo, W, Co, Ni,
etc.)-based biomimetic mimics for [NiFe]-H2ases, but none of
them contain the azadithiolato type of ligand.15−43 Recently,
considering that the bridging azadithiolato ligand in the active
site of [FeFe]-H2ases can play a key role in the catalytic redox
reaction between H2 and protons44−46 and in order to further
develop the biomimetic chemistry of [NiFe]-H2ases, we
decided to prepare the first azadithiolato ligand containing
dinuclear Ni2 complexes in which each of the azadithiolato 4-
RC6H4N(CH2S)2 ligands is bridged between the two Ni atoms
in CpNi and (diphosphine)Ni moieties (Figure 1b).
Fortunately, we have successfully synthesized and structurally
characterized such a type of dinuclear Ni2 complex and in
particular some of them have been found to be catalysts for
INTRODUCTION
■
Hydrogenases (H2ases) constitute a class of metalloenzymes
that catalyze H2 metabolism in a variety of microbes such as
bacteria, archaea, and some eukaryotes.1,2 According to the
metal composition in their active sites, H2ases are usually
divided into three major groups: [NiFe]-H2ases,3−5 [FeFe]-
H2ases,6−8 and [Fe]-H2ase.9−11 An X-ray crystallographic
study demonstrated that the active site of [NiFe]-H2ases
includes two metal centers, in which the Ni center is
coordinated by two terminal cysteinato ligands, the Fe center
is coordinated by one terminal CO and two terminal cyanide
ligands, and the two metal centers are bound together by two
bridging cysteinato ligands (Figure 1a).12−14
Received: February 22, 2020
Figure 1. (a) Active site of [NiFe]-H2ases. (b) Targeted dinuclear Ni2
complexes.
https://dx.doi.org/10.1021/acs.organomet.0c00130
© XXXX American Chemical Society
Organometallics XXXX, XXX, XXX−XXX
A

Organometallics
pubs.acs.org/Organometallics
Article
proton reduction to H2 under CV conditions. Herein, we
report the interesting results obtained in this study.
The new precursor complexes 4−7 are air-stable red solids
and were also characterized by elemental analysis and various
spectroscopic techniques. For instance, the 1H NMR spectra of
4−7 displayed one singlet in the region 4.44−4.50 ppm for the
two CH2 groups in the azadithiolato ligands. The 13C{1H}
NMR spectra showed one singlet in the range 47.4−48.3 ppm
for the two C atoms in the two methylene groups, whereas the
31P{1H} NMR spectra displayed one singlet at ca. 63 and 57
ppm for the two P atoms in the dppv and dppe ligands,
respectively.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the N,N-Bis-
(acetylthiomethyl)-Containing Compounds 4-RC6H4N-
[CH2S(O)CMe]2 (1, R = H; 2, R = Cl; 3, R = MeO). According
to our designed synthetic method for the preparation of the
first azadithiolato-bridged dinuclear Ni2 complexes, we should
first prepare the two types of precursors. The first types of
precursors are the N,N-bis(acetylthiomethyl)-containing ben-
zene derivatives 1−3, which could be prepared in 75−81%
yields by a cocondensation reaction of aniline or its 4-
substituted derivatives 4-RC6H4NH2 with 37% aqueous
formaldedyde and thioacetic acid in EtOH solvent (Scheme 1).
The molecular structure of complex 5 was successfully
determined by X-ray crystal diffraction analysis (Figure 2 and
Scheme 1. Synthesis of Bis(thioester) Precursors 1−3
While the precursor compound 2 is known,47 compounds 1
and 3 are new. 1−3 are all air-stable white solids and were
characterized by elemental analysis and various spectroscopic
methods. For example, the IR spectra of 1−3 showed one
strong absorption band at ca. 1689 cm−1 for their thioester
1
carbonyls. The H NMR spectra displayed two singlets at ca.
Figure 2. Molecular structure of 5 with ellipsoids drawn at the 50%
probability level. All hydrogen atoms are omitted for the sake of
clarity.
2.37 and 5.08 ppm for the CH3CO and CH2 groups in their
N,N-bis(acetylthiomethyl) substituents, respectively. The
13C{1H} NMR spectra exhibited one singlet at ca. 196 ppm
for the thioester carbonyl C atoms.
Table 1). As shown in Figure 2, complex 5 is an azadithiolato
4-ClC6H4N(CH2S)2 and a diphosphine dppv chelated
mononuclear Ni complex. While the dppv ligand is chelated
via its P1 and P2 atoms to the Ni1 atom to constitute an
envelope-shaped five-membered metallacycle, the azadithiolato
ligand is chelated via its S1 and S2 atoms to the Ni1 atom to
construct a boat-shaped six-membered metallacycle that is
axially attached to the 4-chlorophenyl group via the N1 atom.
The bond lengths Ni1−P1 (2.1689 Å), Ni1−P2 (2.1467 Å),
Ni1−S1 (2.1810 Å), and Ni1−S2 (2.1865 Å) in 5 are close to
those corresponding to the previously reported analogue
(dppe)Ni(SCH2)2NC6H4Cl-4.48 The dihedral angle between
the two planes P1Ni1P2 and S1Ni1S2 in 5 is equal to 0.394°,
implying that the Ni1 atom adopts an ideal square-planar
Synthesis and Characterization of the Azadithiolato-
Chelated Mononuclear Ni Complexes (dppv)Ni-
[(SCH2)2NC6H4R-4] (4, R = H; 5, R = Cl) and (dppe)Ni-
[(SCH2)2NC6H4R-4] (6, R = H; 7, R = MeO). The second
types of precursors used for preparing the targeted dinuclear
Ni2 azadithiolates are the azadithiolato ligand chelated
mononuclear Ni complexes 4−7, which were prepared by a
MeCO/Na exchange reaction of the first types of precursors
1−3 with tert-butoxysodium in THF from −78 °C to room
temperature followed by a salt elimination reaction of the
resulting disodium intermediates 4-RC6H4N(CH2SNa)248 with
(dppv)NiCl2 or (dppe)NiCl2 in 41−49% yields, respectively
(Scheme 2).
Scheme 2. Synthesis of Mononuclear Ni Precursors 4−7
B
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Table 1. Selected Bond Lengths (Å) and Angles (deg) for 5
Ni(1)−S(1)
Ni(1)−S(2)
Ni(1)−P(1)
Ni(1)−P(2)
2.1810(9)
2.1865(8)
2.1689(9)
2.1467(10)
N(1)−C(27)
N(1)−C(28)
P(1)−C(13)
P(2)−C(14)
1.431(5)
1.447(4)
1.811(3)
1.823(3)
S(1)−Ni(1)−S(2)
P(1)−Ni(1)−P(2)
P(1)−Ni(1)−S(1)
P(1)−Ni(1)−S(2)
102.67(3)
87.31(3)
85.80(3)
171.53(4)
C(27)−N(1)−C(28)
C(13)−P(1)−Ni(1)
C(14)−P(2)−Ni(1)
C(27)−S(1)−Ni(1)
113.1(3)
108.94(11)
108.81(12)
111.41(12)
geometry. However, in contrast to this, the corresponding
dihydral angle in the previously reported analogue (dppe)Ni-
(SCH2)2NC6H4Cl-4 is 27.6°,48 which implies that its Ni1 atom
is best described as having a distorted-square-planar geometry.
Synthesis and Characterization of the Azadithiolato-
Bridged Dinuclear Ni2 Complexes [(η5-C5H5)Ni{(μ-
SCH2)2NC6H4R-4}Ni(dppv)]BF4 (8, R = H; 9, R = Cl) and
[(η5-C5H5)Ni{(μ-SCH2)2NC6H4R-4}Ni(dppe)]BF4 (10, R = H;
11, R = MeO). Particularly interesting is that the targeted
azadithiolato ligand-bridged dinuclear Ni2 complexes could be
prepared by a coordination reaction of the second types of
precursors 4−7 with the in situ generated cation [η5-C5H5Ni]+
from dissociation of the triple-decker sandwich complex
49
[(C5H5)3Ni2]BF4 in nitromethane at room temperature in
69−92% yields (Scheme 3).
Scheme 3. Synthesis of Targeted Dinuclear Ni2 Complexes
8−11
Figure 3. Molecular structure of 9 with ellipsoids drawn at the 50%
probability level. All hydrogen atoms and the anion BF4− are omitted
for the sake of clarity.
Dinuclear Ni2 complexes 8−11 are air-stable brown solids.
Their elemental analysis and spectral data are in good
agreement with their structures shown in Scheme 3. For
instance, the 1H NMR spectra of 8−11 displayed one singlet in
the range 4.81−5.12 ppm for the five H atoms in the Cp rings
and two doublets in the range 4.12−4.52 ppm for the four H
atoms in their azadithiolato methylene groups. The 13C{1H}
NMR spectra exhibited one singlet at ca. 92 ppm for the five C
atoms in the Cp rings, whereas the 31P{1H} NMR spectra
displayed one singlet at about 70 and 60 ppm for the two P
atoms in the dppv and dppe ligands, respectively.
Figure 4. Molecular structure of 11 with ellipsoids drawn at the 50%
probability level. All hydrogen atoms and the anion BF4− are omitted
for the sake of clarity.
azadithiolato ligand 4-ClC6H4N(CH2S)2 in 9 or 4-
MeOC6H4N(CH2S)2 in 11 is bridged to the Ni1 and Ni2
atoms to construct two fused six-membered metallacycles.
While the metallacycle Ni1S1C6N1C7S2 in 9 adopts a chair
conformation and another metallacycle Ni2S1C6N1C7S2
The molecular structures of complexes 9 and 11 were
unambiguously confirmed by an X-ray crystallographic study
(Figures 3 and 4 and Table 2). As shown in Figures 3 and 4,
both 9 and 11 are monocationic dinuclear Ni2 complexes, each
containing one monocation [CpNi{(μ-SCH2)2NC6H4Cl-4}-
Ni(dppv)]+ or [CpNi{(μ-SCH2)2NC6H4OMe-4}Ni(dppe)]+
adopts
a boat conformation, the metallacycle
Ni1S1C6N1C5S2 in 11 takes a chair conformation and
another metallacycle Ni2S1C6N1C5S2 takes a boat con-
−
and one monoanion BF4 . In the two monocations, the
C
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 9
and 11
Complex 9
Ni(1)−S(1)
Ni(1)−S(2)
Ni(2)−S(1)
Ni(2)−S(2)
2.1825(16)
2.1893(15)
2.2123(15)
2.2086(15)
Ni(2)−P(1)
Ni(2)−P(2)
N(1)−C(6)
P(1)−C(26)
2.1446(16)
2.1651(15)
1.433(6)
1.814(5)
S(1)−Ni(1)−S(2)
S(1)−Ni(2)−S(2)
P(1)−Ni(2)−S(1)
P(1)−Ni(2)−S(2)
89.05(6)
87.80(5)
89.24(6)
175.34(6)
P(1)−Ni(2)−P(2)
Ni(1)−S(1)−C(6)
C(6)−N(1)−C(7)
Ni(2)−P(1)−C(26)
88.26(6)
102.1(2)
113.1(5)
108.66(19)
Complex 11
Ni(1)−S(1)
Ni(1)−S(2)
Ni(2)−S(1)
Ni(2)−S(2)
2.1914(13)
2.1985(14)
2.1986(12)
2.2111(13)
Ni(2)−P(1)
Ni(2)−P(2)
N(1)−C(5)
P(1)−C(25)
2.1792(14)
2.1752(12)
1.423(6)
Figure 5. Cyclic voltammograms of 8 and 9 (1.0 mM) in 0.1 M n-
Bu4NPF6/MeCN at a scan rate of 0.1 V s−1. Arrows indicate the
starting potential and scan direction.
1.844(4)
S(1)−Ni(1)−S(2)
S(1)−Ni(2)−S(2)
P(1)−Ni(2)−S(1)
P(1)−Ni(2)−S(2)
88.92(5)
88.42(5)
90.75(5)
174.38(5)
P(1)−Ni(2)−P(2)
Ni(1)−S(1)−Ni(2)
C(5)−N(1)−C(6)
Ni(2)−P(1)−C(25)
86.82(5)
75.54(4)
115.4(4)
108.65(16)
a MeCN solution of 8 at 0.18 V (1.01 F mol−1 passed in 1 h)
or 9 at 0.20 V (1.08 F mol−1 passed in 1 h). The reduction
events displayed by 8 and 9 each are also one-electron
processes, since their reduction peak current heights are close
to their oxidation peak current heights. While the first
reduction events of 8 and 9 could be assigned to the
CpNiIINiII(dppv)/CpNiINiII(dppv) couple due to the CpNiII
moieties in 8 and 9 each bearing a positive charge, the second
reduction events of 8 and 9 could be attributed to the
CpNiINiII(dppv)/CpNiINiI(dppv) couple since the second
reduction potentials of 8 and 9 are positively shifted relative to
those displayed by their precursors 4 (−1.94 V) and 5 (−1.91
V) (see Figure S1) and in turn the oxidation events of 8 and 9
might be ascribed to the CpNiIINiII(dppv)/CpNiIINiIII(dppv)
couple.51,52,57 It should be noted that all of the reduction and
oxidation waves of complex 9 are positively shifted by 20 mV
relative to those of complex 8, which is consistent with 4-
ClC6H4 group in 9 being an electron-withdrawing group
stronger than the C6H5 group in 8. Additionally, the two
reduction processes of 8 and 9 are all diffusion-controlled,
since their reduction peak currents versus the square root of
the scan rates (25−2000 mV s−1) are linearly correlated (see
Figures S2 and S3).58
formation. The 4-ClC6H4 group in 9 and 4-MeOC6H4 group
in 11 are both bound to the common N1 atom of the
corresponding two fused six-membered rings with an axial type
of bond. It should be noted that (i) the Ni1−Ni2 distances of
9 (2.6781 Å) and 11 (2.6889 Å) are well beyond the sum of
covalent radii of their two Ni atoms (1.24 Å + 1.24 Å = 2.48
Å),50 which implies that no metal−metal bonding exists
between their Ni1 and Ni2 atoms, and (ii) the two Ni1−Ni2
distances in 9 and 11 are much shorter than those of the
reported 1,3-propanedithiolato ligand bridged dinuclear Ni2
analogues Cp2Ni2(μ-pdt) (2.863 Å).35 and [(dppe)2Ni2(μ-
pdt)](BF4)2 (2.871 Å).51
Electrochemical Properties and Electrocatalytic H2-
Producing Ability of Dinuclear Ni2 Complexes 8 and 9.
To date, a variety of homodinuclear Ni2 complexes have been
synthesized and some of them have been found to be
electrocatalytic H2-producing catalysts.51−56 Having prepared
the targeted dinuclear complexes 8−11, we chose complexes 8
and 9 as representatives (due to 8 and 9 having the same types
of structures as those of 10 and 11) to study their
electrochemical properties and electrocatalytic H2-producing
ability. The electrochemical properties of 8 and 9 were
determined by cyclic voltammetric (CV) techniques by using
n-Bu4NPF6 as the supporting electrolyte in MeCN at a scan
rate of 100 mV s−1. As shown in Table 3 and Figure 5,
complexes 8 and 9 display one quasi-reversible reduction wave
at −1.36 and −1.34 V, one irreversible reduction wave at
−1.74 and −1.72 V, and one irreversible oxidation wave at 0.18
and 0.20 V, respectively. Similar to the previously reported
cases,51,52,57 the oxidation events of 8 and 9 each are one-
electron processes, which was confirmed by bulk electrolysis of
To examine if complexes 8 and 9 could have the
electrocatalytic ability for proton reduction to H2, we further
determined their cyclic voltammograms in the presence and
absence (for comparison) of the weak acid HOAc (pKaMeCN
=
22.3, E°HA = 1.35 V).59,60 As shown in Figures 6 and 7, when
1−20 mM HOAc is sequentially added to MeCN solutions of
8 and 9, the current heights of their original first reduction
waves remain unchanged. However, in contrast to this, when
1−20 mM HOAc is sequentially added, the current heights of
their original second reduction waves are considerably
increased. Apparently, such an observation features an
electrocatalytic process for proton reduction to hydro-
gen.52,61,62 Furthermore, as shown in Figures 6 and 7, when
1−8 mM HOAc is continuously added, the original second
reduction waves are positively shifted by about 40 mV, which is
most likely caused by protonation of the central N atoms in
their bridged azadithiolato ligands.63
a
Table 3. Electrochemical Data of 8 and 9
compound
E
pc1/V
E
pc2/V
Epa/V
8
9
−1.36
−1.34
−1.74
−1.72
0.18
0.20
In order to evaluate the electrocatalytic ability of 8 and 9, we
determined the ratio of the catalytic current (icat) to reductive
peak current (ip) in the absence of the added acid (note that a
higher icat/ip value means a faster catalysis).62,64,65 At a
a
All potentials are versus Fc/Fc+ in 0.1 M n-Bu4NPF6/MeCN at a
scan rate of 0.1 V s−1.
D
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
(TONs) of 9.5 and 9.7, respectively. Analysis by gas
chromatography (GC) showed that the yields of H2 evolved
during the bulk electrolysis catalyzed by 8 and 9 are all above
90%.
SUMMARY AND CONCLUSIONS
■
On the basis of preparation of the bis(thioester) precursors 1−
3 and mononuclear Ni precursors 4−7, the first azadithiolato-
bridged dinuclear Ni2 complexes 8−11 have been synthesized
by a coordination reaction of mononuclear Ni complexes 4−7
with the monocation CpNi+ generated in situ from the triple-
decker sandwich complex (Cp3Ni2)BF4. The spectroscopic
characterization of all the targeted complexes 8−11 and the X-
ray crystallographic characterization of their two representa-
tives 9 and 11 have proved that they all contain one
azadithiolato ligand 4-RC6H4N(CH2S)2 (R = H, Cl, MeO)
that is bridged between the two Ni atoms in CpNi and (dppv)
Ni or (dppe)Ni moieties. In addition, on the basis of
electrochemical and electrocatalytic studies, we have found
that targeted complexes 8 and 9 can serve as the catalysts for
proton reduction to H2 using HOAc as the proton source
under CV conditions. Finally, it should be indicated that (i)
the azadithiolato-bridged dinuclear complexes 8 and 9 are
better catalysts than the dithiolato-bridged dinuclear com-
plexes Cp2Ni2(μ-SR)2 (R = PhCH2, C8H17, C6H4Me) for the
H2 production from HOAc under the electrochemical
conditions, since the former have much higher icat/ip values
and much lower overpotentials in comparison to those of the
latter, and (ii) in view of the structural similarity of our
targeted dinuclear complexes 8−11 with the active site of
[NiFe]-H2ases as well as the catalytic functional similarity of
the representative targeted complexes 8 and 9 with [NiFe]-
H2ases, the targeted complexes reported in this article could be
regarded as biomimetic mimics for [NiFe]-H2ases.
Figure 6. Cyclic voltammograms of 8 (1.0 mM) with HOAc (0−20
mM) in 0.1 M n-Bu4NPF6/MeCN at a scan rate of 0.1 V s−1.
Figure 7. Cyclic voltammograms of 9 (1.0 mM) with HOAc (0−20
mM) in 0.1 M n-Bu4NPF6/MeCN at a scan rate of 0.1 V s−1.
EXPERIMENTAL SECTION
■
General Comments. All reactions were performed using standard
Schlenk and vacuum-line techniques under an atmosphere of argon.
Tetrahydrofuran (THF) was distilled under Ar from sodium/
benzophenone ketyl, whereas methylene chloride was distilled
under Ar from CaH2. Ethanol, MeNO2, t-BuONa, 4-RC6H4NH2 (R
= H, Cl, MeO), thioacetic acid, and 37% aqueous formaldehyde were
available commercially, whereas [(C5H5)3Ni2]BF4,49 (dppv)NiCl2
(dppv = 1,2-bis(diphenylphosphino)ethane),68 and (dppe)NiCl2
(dppe = 1,2-bis(diphenylphosphino)ethane)68 were prepared accord-
concentration of 20 mM HOAc, the icat/ip values for 8 and 9
were calculated to be 20.3 and 18.2, respectively. It follows that
the icat/ip values of the azadithiolato-bridged dinuclear Ni2
complexes 8 and 9 are much higher than those (7.8−12.2) of
the previously reported dithiolato-bridged dinuclear complexes
Cp2Ni2(μ-SR)2 (R = PhCH2, C8H17, C6H4Me).52 In addition,
considering that overpotential (defined as the difference
between the potential at the half-maximum of the catalytic
current and the standard potential E°HA of the acid) is also an
important parameter for evaluating the electrocatalytic ability
for a catalyst (note that a better catalyst has a lower
overpotential),66,67 we further determined the overpotentials
of 8 and 9 by using the Evans method.59 At a concentration of
20 mM HOAc, the overpotentials of 8 and 9 were calculated to
be 0.33 and 0.30 V, respectively (see Figures 6 and 7). It
follows that the overpotentials of the azadithiolato-bridged
dinuclear Ni2 complexes 8 and 9 are much lower than those
(0.57−0.61 V) of the previously reported dithiolato-bridged
dinuclear Ni2 complexes.52
ing to the published procedures. While H, 13C{1H}, and 31P{1H}
1
NMR spectra were obtained on a Bruker Avance 400 NMR
spectrometer, IR spectra were recorded on a Bio-Rad FTS 135
infrared spectrophotometer. Elemental analyses were performed on an
Elementar Vario EL analyzer. Melting points were determined on a
SGW X-4 microscopic melting point apparatus and were uncorrected.
Preparation of C6H5N[CH2S(O)CMe]2 (1). A 250 mL three-
necked flask was charged with aniline (9.1 mL, 100 mmol), 37%
aqueous formaldehyde (24.2 mL, 320 mmol), thioacetic acid (14.6
mL, 200 mmol), and ethanol (100 mL). While it was stirred, the
mixture was heated to about 60 °C and stirred at this temperature for
3 h. To the resulting mixture was added 100 mL of ice−water to give
precipitates. The precipitates were collected by filtration, washed with
some cold ethanol, and finally dried under vacuum to give 1 (21.7 g,
81%) as a white solid, mp 66−67 °C. Anal. Calcd for C12H15NO2S2:
C, 53.51; H, 5.61; N, 5.20. Found: C, 53.55; H, 5.76; N, 5.23. IR
(KBr disk): νCO 1690 (vs) cm−1. 1H NMR (400 MHz, CDCl3): 2.38
(s, 6H, 2CH3), 5.12 (s, 4H, CH2NCH2), 6.77−7.31 (m, 5H, C6H5)
ppm. 13C{1H} NMR (100 MHz, CDCl3): 31.4 (s, CH3), 52.9 (s,
CH2NCH2), 114.6−144.0 (m, C6H5), 196.0 (s, CO) ppm.
Finally, it should be indicated that the electrocatalytic H2
production catalyzed by 8 and 9 was proved by electrolysis of a
MeCN solution of 8 or 9 (1.0 mM) with an excess amount of
HOAc (50 mM) at −1.90 V. During 1 h of electrolysis, totals
of 19.0 and 19.4 F mol−1 passed through the electrolysis cell,
respectively; this corresponds to theoretical turnover numbers
E
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Preparation of (4-ClC6H4)N[CH2S(O)CMe]2 (2). The same
procedure was followed as for 1, except that 4-chloroaniline (12.8
g, 100 mmol) was used instead of aniline. 2 (23.7 g, 78%) was
obtained as a white solid, mp 82−83 °C. Anal. Calcd for
C12H14ClNO2S2: C, 47.44; H, 4.64; N, 4.61. Found: C, 47.33; H,
NMR (100 MHz, CDCl3): 27.8−28.3 (m, CH2CH2), 48.3 (s,
CH2NCH2), 55.9 (s, OCH3), 114.1−151.9 (m, C6H5, C6H4) ppm.
31P{1H} NMR (162 MHz, CDCl3): 57.3 (s, NiP2) ppm.
Preparation of [(η5-C5H5)Ni{(μ-SCH2)2NC6H5}Ni(dppv)]BF4
(8). A 50 mL three-necked flask was charged with (dppv)Ni-
[(SCH2)2NC6H5] (0.128 g, 0.2 mmol), [(C5H5)3Ni2]BF4 (0.080 g,
0.2 mmol), and MeNO2 (10 mL). The mixture was stirred at room
temperature for 0.5 h to give a brown-red solution. The solvent was
removed at reduced pressure to leave a residue, which was subjected
to column chromatography (silica gel). Elution with CH2Cl2/acetone
(10/1 v/v) developed a brown band, from which 8 (0.117 g, 69%)
was obtained as a brown solid, mp 92−93 °C. Anal. Calcd for
C39H36BF4NNi2P2S2: C, 55.18; H, 4.27; N, 1.65. Found: C, 54.98; H,
4.32; N, 1.40. IR (KBr disk): 1495 (s), 1438 (s), 1268 (s), 1059 (vs),
738 (vs) cm−1. 1H NMR (400 MHz, CDCl3): 4.26, 4.52 (dd, J = 11.4
Hz, 4H, CH2NCH2), 4.81 (s, 5H, C5H5), 6.50−7.81 (m, 27H, 5C6H5,
CHCH) ppm. 13C{1H} NMR (100 MHz, CDCl3): 55.1 (s,
CH2NCH2), 91.8 (s, C5H5), 118.0−146.5 (m, C6H5, CHCH) ppm.
31P{1H} NMR (162 MHz, CDCl3): 70.0 (s, NiP2) ppm.
1
4.74; N, 4.52. IR (KBr disk): νCO 1690 (vs) cm−1. H NMR (400
MHz, CDCl3): 2.37 (s, 6H, 2CH3), 5.06 (s, 4H, CH2NCH2), 6.68−
7.23 (m, 4H, C6H4) ppm. 13C{1H} NMR (100 MHz, CDCl3): 31.3
(s, CH3), 52.8 (s, CH2NCH2), 115.8−142.5 (m, C6H4), 195.8 (s,
CO) ppm.
Preparation of (4-MeOC6H4)N[CH2S(O)CMe]2 (3). The same
procedure was followed as for 1, except that 4-methoxyaniline (12.3 g,
100 mmol) was utilized instead of aniline. 3 (22.4 g, 75%) was
obtained as a white solid, mp 73−74 °C. Anal. Calcd for
C13H17NO3S2: C, 52.15; H, 5.72; N, 4.68. Found: C, 52.26; H,
1
5.90; N, 4.61. IR (KBr disk): νCO 1687 (vs) cm−1. H NMR (400
MHz, CDCl3): 2.36 (s, 6H, 2CH3CO), 3.76 (s, 3H, OCH3), 5.07
(s, 4H, CH2NCH2), 6.74−6.86 (m, 4H, C6H4) ppm. 13C{1H} NMR
(100 MHz, CDCl3): 31.4 (s, CH3CO), 53.7 (s, CH2NCH2), 55.7
(s, OCH3), 114.9−154.1 (m, C6H4), 196.1 (s, CO) ppm.
Preparation of [(η5-C5H5)Ni{(μ-SCH2)2NC6H4Cl-4}Ni(dppv)]-
(BF4) (9). The same procedure was followed as for 8, except that
(dppv)Ni[(SCH2)2NC6H5] was replaced by (dppv)Ni-
[(SCH2)2NC6H4Cl-4] (0.135 g, 0.2 mmol). 9 (0.159 g, 90%) was
obtained as a brown solid, mp 247 °C dec. Anal. Calcd for
C39H35BClF4NNi2P2S2: C, 53.02; H, 3.99; N, 1.59. Found: C, 53.29;
H, 3.73; N, 1.50. IR (KBr disk):1492 (s), 1437 (s), 1267 (s), 1057
(vs), 738 (vs) cm−1. 1H NMR (400 MHz, CDCl3): 4.20, 4.51 (dd, J =
12.2 Hz, 4H, CH2NCH2), 4.91 (s, 5H, C5H5), 6.32−7.87 (m, 26H,
4C6H5, C6H4, CHCH) ppm. 13C{1H} NMR (100 MHz, CDCl3):
54.9 (s, CH2NCH2), 92.1 (s, C5H5), 119.2−147.1 (m, C6H5, C6H4,
CHCH) ppm. 31P{1H} NMR (162 MHz, CDCl3): 70.2 (s, NiP2)
ppm.
Preparation of (dppv)Ni[(SCH2)2NC6H5] (4). A 100 mL three-
necked flask was charged with C6H5N[CH2S(O)CMe]2 (0.269 g, 1.0
mmol), t-BuONa (0.192 g, 2.0 mmol), and THF (40 mL). The
mixture was stirred at −78 °C for 3 h to give a pale yellow solution.
To this solution was slowly added (dppv)NiCl2(0.526 g, 1.0 mmol) in
10 mL of THF to give a brown-red solution. After the brown-red
solution was stirred at −78 °C for 4 h, it was warmed to room
temperature and stirred at this temperature for 1 h. The solvent was
removed at reduced pressure, and the residue was subjected to
column chromatography (silica gel). Elution with CH2Cl2/acetone
(25/1 v/v) developed a red band, from which 4 (0.313 g, 49%) was
obtained as a red solid, mp 197−198 °C. Anal. Calcd for
C34H31NNiP2S2: C, 63.97; H, 4.89; N, 2.19. Found: C, 63.77; H,
4.91; N, 2.15. IR (KBr disk): 1496 (m), 1434 (m), 1265 (s), 1099 (s),
Preparation of [(η5-C5H5)Ni{(μ-SCH2)2NC6H5}Ni(dppe)]BF4
(10). The same procedure was followed as for 8, except that
(dppv)Ni[(SCH2)2NC6H5] was replaced by (dppe)Ni-
[(SCH2)2NC6H5] (0.128 g, 0.2 mmol). 10 (0.157 g, 92%) was
obtained as a brown solid, mp 117−118 °C. Anal. Calcd for
C39H38BF4NNi2P2S2: C, 55.04; H, 4.50; N, 1.65. Found: C, 55.30; H,
4.37; N, 1.43. IR (KBr disk): 1642 (m), 1431 (m), 1267 (s), 1057
1037 (s) cm−1 1H NMR (400 MHz, CDCl3): 4.44 (s, 4H,
.
CH2NCH2), 6.77−7.52 (m, 27H, 5C6H5, CHCH) ppm. 13C{1H}
NMR (100 MHz, CDCl3): 48.0 (s, CH2NCH2), 117.6−149.2 (m,
C6H5, CHCH) ppm. 31P{1H} NMR (162 MHz, CDCl3): 63.3 (s,
NiP2) ppm.
1
(vs), 740 (vs) cm−1. H NMR (400 MHz, CDCl3): 2.54−2.64 (m,
Preparation of (dppv)Ni[(SCH2)2NC6H4Cl-4] (5). The same
procedure as for 4 was followed, except that C6H5N[CH2S(O)CMe]2
was replaced by (4-ClC6H4)N[CH2S(O)CMe]2 (0.304 g, 1.0 mmol).
5 (0.276 g, 41%) was obtained as a red solid, mp 158−159 °C. Anal.
Calcd for C34H30ClNNiP2S2: C, 60.69; H, 4.49; N, 2.08. Found: C,
60.39; H, 4.65; N, 1.78. IR (KBr disk): 1494 (m), 1434 (m), 1267
4H, CH2CH2), 4.21, 4.46 (dd, J = 12.0 Hz, 4H, CH2NCH2), 5.05 (s,
5H, C5H5), 6.48−7.95 (m, 25H, 5C6H5) ppm. 13C{1H} NMR (100
MHz, CDCl3): 27.1−27.6 (m, CH2CH2), 55.1 (s, CH2NCH2), 92.1
(s, C5H5), 118.1−143.9 (m, C6H5) ppm. 31P{1H} NMR (162 MHz,
CDCl3): 61.4 (s, NiP2) ppm.
1
(s), 1053 (vs) cm−1. H NMR (400 MHz, CDCl3): 4.47 (s, 4H,
Preparation of [(η5-C5H5)Ni{(μ-SCH2)2NC6H4OMe-4}Ni-
(dppe)]BF4 (11). The same procedure was followed as for 10,
except that (dppe)Ni[(SCH2)2NC6H5] was replaced by (dppe)Ni-
[(SCH2)2NC6H4OMe-4] (0.134 g, 0.2 mmol). 11 (0.143 g, 81%) was
obtained as a brown solid, mp 104−105 °C. Anal. Calcd for
C40H40BF4NNi2OP2S2: C, 54.53; H, 4.58; N, 1.59. Found: C, 54.29;
H, 4.71; N, 1.42. IR (KBr disk): 1643 (m), 1430 (m), 1266 (s), 1057
CH2NCH2), 6.83−7.62 (m, 26H, 4C6H5, C6H4, CHCH) ppm.
13C{1H} NMR (100 MHz, CDCl3): 48.2 (s, CH2NCH2), 119.3−
147.1 (m, C6H5, C6H4, CHCH) ppm. 31P{1H} NMR (162 MHz,
CDCl3): 63.3 (s, NiP2) ppm.
Preparation of (dppe)Ni[(SCH2)2NC6H5] (6). The same
procedure as for 4 was followed, except that (dppv)NiCl2 was
replaced by (dppe)NiCl2 (0.528 g, 1.0 mmol). 6 (0.290 g, 45%) was
obtained as a red solid, mp 120 °C dec. Anal. Calcd for
C34H33NNiP2S2: C, 63.77; H, 5.19; N, 2.19. Found: C, 63.88; H,
5.29; N, 2.25. IR (KBr disk): 1594 (m), 1496 (m), 1435 (s), 1098
1
(vs), 740 (vs) cm−1. H NMR (400 MHz, CDCl3): 2.51−2.54 (m,
4H, CH2CH2), 3.77 (s, 3H, OCH3), 4.12, 4.50 (dd, J = 11.8 Hz, 4H,
CH2NCH2), 5.12 (s, 5H, C5H5), 6.38−8.00 (m, 24H, 4C6H5, C6H4)
ppm. 13C{1H} NMR (100 MHz, CDCl3): 27.0−27.5 (m, CH2CH2),
55.7 (s, CH2NCH2), 56.5 (s, OCH3), 92.0 (s, C5H5), 114.9−154.7
(m, C6H5, C6H4) ppm. 31P{1H} NMR (162 MHz, CDCl3): 60.8 (s,
NiP2) ppm.
1
(vs), 1059 (vs) cm−1. H NMR (400 MHz, CDCl3): 2.05, 2.09 (2s,
4H, CH2CH2), 4.50 (s, 4H, CH2NCH2), 6.87−7.68 (m, 25H, 5C6H5)
ppm. 13C{1H} NMR (100 MHz, CDCl3): 27.7−28.2 (m, CH2CH2),
47.4 (s, CH2NCH2), 117.4−145.9 (m, C6H5) ppm. 31P{1H} NMR
(162 MHz, CDCl3): 56.6 (s, NiP2) ppm.
Preparation of (dppe)Ni[(SCH2)2NC6H4OMe-4] (7). The same
procedure was followed as for 6, except that C6H5N[CH2S(O)CMe]2
was replaced by (4-MeOC6H4)N[CH2S(O)CMe]2 (0.299 g, 1.0
mmol). 7 (0.288 g, 43%) was obtained as a red solid, mp 143−144
°C. Anal. Calcd for C35H35NNiOP2S2: C, 62.70; H, 5.26; N, 2.09.
Found: C, 62.53; H, 5.32; N, 2.08. IR (KBr disk): 1510 (vs), 1435
(s), 1273 (s), 1101 (vs), 1041 (vs) cm−1. 1H NMR (400 MHz,
CDCl3): 2.05, 2.09 (2s, 4H, CH2CH2), 3.88 (s, 3H, OCH3), 4.47 (s,
4H, CH2NCH2), 6.85−7.70 (m, 24H, 4C6H5, C6H4) ppm. 13C{1H}
X-ray Crystal Structure Determinations of 5, 9, and 11.
White single crystals of 5, 9, and 11 for X-ray diffraction analysis were
grown by slow diffusion of hexane into their CH2Cl2 solutions at −5
°C. A single crystal of 5, 9, or 11 was mounted on a Rigaku MM-007
(rotating anode) diffractometer equipped with an AtlasS2 accessory.
While the data for 5 and 11 were collected using a confocal
monochromator with Cu Kα radiation (λ = 1.54184 Å) in the ω
scanning mode at 156 and 137 K, respectively, data for 9 were
collected using a confocal monochromator with Mo Kα radiation (λ =
0.71073 Å) in the ω scanning mode at 293 K. Data collection,
reduction, and absorption correction were performed by the
F
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
Table 4. Crystal Data and Structure Refinement Details for 5, 9, and 11
5
9
11
mol formula
mol wt
cryst syst
space group
a/Å
b/Å
c/Å
α/deg
C34H30ClNNiP2S2
672.81
C39H35BClF4NNi2P2S2
883.42
orthorhombic
P212121
10.8883(6)
14.1424(6)
24.6398(12)
90
C40H40BF4NNi2OP2S2·CH2Cl2
965.94
monoclinic
P121/n1
13.7926(6)
20.2017(8)
14.8223(6)
90
monoclinic
P121/c1
9.7904(3)
22.7021(6)
14.9176(3)
90
β/deg
γ/deg
V/Å3
100.961(3)
90
3255.14(15)
4
90
90
91.602(3)
90
4128.4(3)
4
3794.2(3)
4
Z
Dc/g cm−3
abs coeff/mm−1
F(000)
index ranges
1.373
3.926
1392
−11 ≤ h ≤ 11
−24 ≤ k ≤ 27
−17 ≤ l ≤ 12
12434
1.547
1.308
1808
−12 ≤ h ≤ 12
−16 ≤ k ≤ 14
−29 ≤ l ≤ 25
16389
1.554
4.450
1984
−16 ≤ h ≤ 12
−17 ≤ k ≤ 23
−13 ≤ l ≤ 17
14646
no. of rflns
no. of indep rflns
5812
6670
6788
2θmax/deg
134.15
50.02
127.37
R
0.0522
0.0406
0.0699
Rw
0.1426
0.0731
0.1884
GOF
1.031
0.847/−0.578
1.010
0.451/−0.490
1.042
1.996 /−0.646
largest diff peak, hole/e Å−3
CRYSTALCLEAR program.69 The structures were solved by direct
methods using the SHELXS program70 and refined by full-matrix
least-squares techniques (SHELXL)71 on F2. Hydrogen atoms were
located by using the geometric method. Details of crystal data, data
collections, and structure refinements are summarized in Table 4.
Authors
Wen-Bo Liu − Department of Chemistry, State Key Laboratory
of Elemento-Organic Chemistry, College of Chemistry, Nankai
University, Tianjin 300071, People’s Republic of China
Bei-Bei Liu − Department of Chemistry, State Key Laboratory of
Elemento-Organic Chemistry, College of Chemistry, Nankai
University, Tianjin 300071, People’s Republic of China
ASSOCIATED CONTENT
■
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00130
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00130.
Notes
The authors declare no competing financial interest.
Electrochemical and electrocatalytic data, overpotential
determinations, and IR and NMR spectra of compounds
3, 4, 6, and 8−11 (PDF)
ACKNOWLEDGMENTS
■
We are grateful to the National Natural Science Foundation of
China (21772106) and Technology of China (973 program
2014CB845604) for financial support.
Accession Codes
CCDC 1984978−1984980 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
REFERENCES
■
(1) Adams, M. W. W.; Stiefel, E. I. Biological Hydrogen Production:
Not So Elementary. Science 1998, 282, 1842−1843.
(2) Cammack, R. Hydrogenase sophistication. Nature 1999, 397,
214−215.
(3) Albracht, S. P. J. Nickel hydrogenases: in search of the active site.
Biochim. Biophys. Acta, Bioenerg. 1994, 1188, 167−204.
(4) Fontecilla-Camps, J. C.; Volbeda, A.; Cavazza, C.; Nicolet, Y.
Structure/Function Relationships of [NiFe]- and [FeFe]-Hydro-
genases. Chem. Rev. 2007, 107, 4273−4303.
AUTHOR INFORMATION
■
Corresponding Author
Li-Cheng Song − Department of Chemistry, State Key
Laboratory of Elemento-Organic Chemistry, College of
Chemistry, Nankai University, Tianjin 300071, People’s
Republic of China; Collaborative Innovation Center of
Chemical Science and Engineering (Tianjin), Tianjin 300072,
People’s Republic of China; orcid.org/0000-0003-0964-
8869; Email: lcsong@nankai.edu.cn
(5) Bouwman, E.; Reedijk, J. Structural and functional models
related to the nickel hydrogenases. Coord. Chem. Rev. 2005, 249,
1555−1581.
(6) Nicolet, Y.; Lemon, B. J.; Fontecilla-Camps, J. C.; Peters, J. W. A
novel FeS cluster in Fe-only hydrogenases. Trends Biochem. Sci. 2000,
25, 138−143.
G
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
(7) Evans, D. J.; Pickett, C. J. Chemistry and the hydrogenases.
Chem. Soc. Rev. 2003, 32, 268−275.
(27) Sellmann, D.; Lauderbach, F.; Heinemann, F. W. Trinuclear
[NiFe] Clusters as Structural Models for [NiFe] Hydrogenase Active
Sites. Eur. J. Inorg. Chem. 2005, 2005, 371−377.
(28) Ogo, S.; Ichikawa, K.; Kishima, T.; Matsumoto, T.; Nakai, H.;
Kusaka, K.; Ohhara, T. A Functional [NiFe]Hydrogenase Mimic That
Catalyzes Electron and Hydride Transfer from H2. Science 2013, 339,
682−684.
(29) Ohki, Y.; Yasumura, K.; Ando, M.; Shimokata, S.; Tatsumi, K.
A model for the CO-inhibited form of [NiFe] hydrogenase: synthesis
of (CO)3Fe(μ-StBu)3Ni{SC6H3-2,6-(mesityl)2} and reversible CO
addition at the Ni site. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 3994−
3997.
(8) Frey, M. Hydrogenases: Hydrogen-Activating Enzymes.
ChemBioChem 2002, 3, 153−160.
(9) Shima, S.; Pilak, O.; Vogt, S.; Schick, M.; Stagni, M. S.; Meyer-
Klaucke, W.; Warkentin, E.; Thauer, R. K.; Ermler, U. The Crystal
Structure of [Fe]-Hydrogenase Reveals the Geometry of the Active
Site. Science 2008, 321, 572−575.
(10) Shima, S.; Thauer, R. K. A Third Type of Hydrogenase
Catalyzing H2 Activation. Chem. Rec. 2007, 7, 37−46.
(11) Wright, J. A.; Turrell, P. J.; Pickett, C. J. The Third
Hydrogenase: More Natural Organometallics. Organometallics 2010,
29, 6146−6156.
(30) Ogo, S.; Kabe, R.; Uehara, K.; Kure, B.; Nishimura, T.; Menon,
S. C.; Harada, R.; Fukuzumi, S.; Higuchi, Y.; Ohhara, T.; Tamada, T.;
Kuroki, R. A Dinuclear Ni(μ-H)Ru Complex Derived from H2. Science
2007, 316, 585−587.
(12) Volbeda, A.; Charon, M.-H.; Piras, C.; Hatchikian, E. C.; Frey,
M.; Fontecilla-Camps, J. C. Crystal structure of the nickel-iron
hydrogenase from Desulfovibrio gigas. Nature 1995, 373, 580−587.
(13) Volbeda, A.; Garcin, E.; Piras, C.; de Lacey, A. L.; Fernandez, V.
M.; Hatchikian, E. C.; Frey, M.; Fontecilla-Camps, J. C. Structure of
the [NiFe] Hydrogenase Active Site: Evidence for Biologically
Uncommon Fe Ligands. J. Am. Chem. Soc. 1996, 118, 12989−12996.
(14) Higuchi, Y.; Ogata, H.; Miki, K.; Yasuoka, N.; Yagi, T. Removal
of the bridging ligand atom at the Ni-Fe active site of [NiFe]
hydrogenase upon reduction with H2, as revealed by X-ray structure
analysis at 1.4 Å resolution. Structure 1999, 7, 549−556.
(31) Brazzolotto, D.; Gennari, M.; Queyriaux, N.; Simmons, T. R.;
́
Pecaut, J.; Demeshko, S.; Meyer, F.; Orio, M.; Artero, V.; Duboc, C.
Nickel-centred proton reduction catalysis in a model of [NiFe]
hydrogenase. Nat. Chem. 2016, 8, 1054−1060.
(32) Song, L.-C.; Yang, X.-Y.; Cao, M.; Gao, X.-Y.; Liu, B.-B.; Zhu,
L.; Jiang, F. Dithiolato-bridged nickel-iron complexes as models for
the active site of [NiFe]-hydrogenases. Chem. Commun. 2017, 53,
3818−3821.
(15) Lubitz, W.; Ogata, H.; Rudiger, O.; Reijerse, E. Hydrogenases.
̈
Chem. Rev. 2014, 114, 4081−4148.
(33) Song, L.-C.; Yang, X.-Y.; Gao, X.-Y.; Cao, M. Nickel-Iron
Dithiolato Hydrides Derived from H2 Activation by Their μ-Hydroxo
Ligand-Containing Analogues. Inorg. Chem. 2019, 58, 39−42.
(16) Schilter, D.; Camara, J. M.; Huynh, M. T.; Hammes-Schiffer, S.;
Rauchfuss, T. B. Hydrogenase Enzymes and Their Synthetic Models:
The Role of Metal Hydrides. Chem. Rev. 2016, 116, 8693−8749.
(17) Simmons, T. R.; Berggren, G.; Bacchi, M.; Fontecave, M.;
Artero, V. Mimicking hydrogenases: From biomimetics to artificial
enzymes. Coord. Chem. Rev. 2014, 270−271, 127−150.
́
(34) Lindenmaier, N. J.; Wahlefeld, S.; Bill, E.; Szilvasi, T.; Eberle,
C.; Yao, S.; Hildebrandt, P.; Horch, M.; Zebger, I.; Driess, M. An S-
Oxygenated [NiFe] Complex Modelling Sulfenate Intermediates of an
O2-Tolerant Hydrogenase. Angew. Chem., Int. Ed. 2017, 56, 2208−
2211.
(18) Ogo, S. H2 and O2 activation by [NiFe]hydrogenases-Insights
from model complexes. Coord. Chem. Rev. 2017, 334, 43−53.
(19) Zhu, W.; Marr, A. C.; Wang, Q.; Neese, F.; Spencer, D. J. E.;
(35) Chambers, G. M.; Rauchfuss, T. B.; Arrigoni, F.; Zampella, G.
Effect of Pyramidalization of the M2(SR)2 Center: The Case of
(C5H5)2Ni2(SR)2. Organometallics 2016, 35, 836−846.
̈
Blake, A. J.; Cooke, P. A.; Wilson, C.; Schroder, M. Modulation of the
(36) Schilter, D.; Fuller, A. L.; Gray, D. L. Nickel-Molybdenum and
Nickel-Tungsten Dithiolates: Hybrid Models for Hydrogenases and
Hydrodesulfurization. Eur. J. Inorg. Chem. 2015, 2015, 4638−4642.
(37) Rosenkoetter, K. E.; Ziller, J. W.; Heyduk, A. F. A
Heterobimetallic W-Ni Complex Containing a Redox-Active W-
[SNS]2 Metalloligand. Inorg. Chem. 2016, 55, 6794−6798.
(38) Song, L.-C.; Zhang, L.-D.; Zhang, W.-W.; Liu, B.-B.
Heterodinuclear Ni/M (M = Mo, W) Complexes Relevant to the
Active Site of [NiFe]-Hydrogenases: Synthesis, Characterization, and
Electrocatalytic H2 Evolution. Organometallics 2018, 37, 1948−1957.
(39) Ogo, S.; Mori, Y.; Ando, T.; Matsumoto, T.; Yatabe, T.; Yoon,
K.-S.; Hayashi, H.; Asano, M. One Model, Two Enzymes: Activation
of Hydrogen and Carbon Monoxide. Angew. Chem., Int. Ed. 2017, 56,
9723−9726.
(40) Kure, B.; Sano, M.; Watanabe, N.; Nakajima, T.; Tanase, T.
Synthesis and Reactivity of Thiolate-Bridged NiIIMI Heterodinuclear
Complexes (M = Rh, Ir) with an S-Bidentate NiP2S2 Metalloligand.
Eur. J. Inorg. Chem. 2017, 2017, 4097−4109.
(41) Fourmond, V.; Canaguier, S.; Golly, B.; Field, M. J.; Fontecave,
M.; Artero, V. A nickel-manganese catalyst as a biomimic of the active
site of NiFe hydrogenases: a combined electrocatalytical and DFT
mechanistic study. Energy Environ. Sci. 2011, 4, 2417−2427.
(42) Song, L.-C.; Li, J.-P.; Xie, Z.-J.; Song, H.-B. Synthesis, Structural
Characterization, and Electrochemical Properties of Dinuclear Ni/Mn
Model Complexes for the Active Site of [NiFe]-Hydrogenases. Inorg.
Chem. 2013, 52, 11618−11626.
electronic structure and the Ni-Fe distance in heterobimetallic models
for the active site in [NiFe]hydrogenase. Proc. Natl. Acad. Sci. U. S. A.
2005, 102, 18280−18285.
(20) Wang, Q.; Barclay, J. E.; Blake, A. J.; Davies, E. S.; Evans, D. J.;
̈
Marr, A. C.; McInnes, E. J. L.; McMaster, J.; Wilson, C.; Schroder, M.
The Synthesis and Electronic Structure of a Novel [NiS4Fe2(CO)6]
Radical Cluster: Implications for the Active Site of the [NiFe]
Hydrogenases. Chem. - Eur. J. 2004, 10, 3384−3396.
(21) Osterloh, F.; Saak, W.; Haase, D.; Pohl, S. Synthesis, X-ray
structure and electrochemical characterisation of a binuclear thiolate
bridged Ni-Fe-nitrosyl complex, related to the active site of NiFe
hydrogenase. Chem. Commun. 1997, 979−980.
(22) Yang, X.; Elrod, L. C.; Reibenspies, J. H.; Hall, M. B.;
Darensbourg, M. Y. Oxygen uptake in complexes related to [NiFeS]-
and [NiFeSe]-hydrgenase active sites. Chem. Sci. 2019, 10, 1368−
1373.
(23) Carroll, M. E.; Barton, B. E.; Gray, D. L.; Mack, A. E.;
Rauchfuss, T. B. Active-Site Models for the Nickel-Iron Hydro-
genases: Effects of Ligands on Reactivity and Catalytic Properties.
Inorg. Chem. 2011, 50, 9554−9563.
(24) Smith, M. C.; Barclay, J. E.; Cramer, S. P.; Davies, S. C.; Gu,
W.-W.; Hughes, D. L.; Longhurst, S.; Evans, D. J. Nickel-iron-sulfur
complexes: approaching structural analogues of the active sites of
NiFe-hydrogenase and carbon monoxide dehydrogenase/acetyl-CoA
synthase. J. Chem. Soc., Dalton Trans. 2002, 2641−2647.
(25) Verhagen, J. A. W.; Lutz, M.; Spek, A. L.; Bouwman, E.
Synthesis and Characterisation of New Nickel-Iron Complexes with
an S4 Coordination Environment around the Nickel Centre. Eur. J.
Inorg. Chem. 2003, 2003, 3968−3974.
(26) Li, Z.; Ohki, Y.; Tatsumi, K. Dithiolato-Bridged Dinuclear Iron-
Nickel Complexes [Fe(CO)2(CN)2(μ-SCH2CH2CH2S)Ni-
(S2CNR2)]− Modeling the Active Site of [NiFe] Hydrogenase. J.
Am. Chem. Soc. 2005, 127, 8950−8951.
(43) Chu, X.; Jin, J.; Ming, B.; Pang, M.; Yu, X.; Tung, C.-H.; Wang,
W. Bimetallic nickel-cobalt hydrides in H2 activation and catalytic
proton reduction. Chem. Sci. 2019, 10, 761−767.
(44) Fan, H.-J.; Hall, M. B. A Capable Bridging Ligand for Fe-Only
Hydrogenase: Density Functional Calculations of a Low-Energy
Route for Heterolytic Cleavage and Formation of Dihydrogen. J. Am.
Chem. Soc. 2001, 123, 3828−3829.
H
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
(45) Silakov, A.; Wenk, B.; Reijerse, E.; Lubitz, W. 14N HYSCORE
investigation of the H-cluster of [FeFe] hydrogenase: evidence for a
nitrogen in the dithiol bridge. Phys. Chem. Chem. Phys. 2009, 11,
6592−6599.
(46) Berggren, G.; Adamska, A.; Lambertz, C.; Simmons, T. R.;
Esselborn, J.; Atta, M.; Gambarelli, S.; Mouesca, J.-M.; Reijerse, E.;
Lubitz, W.; Happe, T.; Artero, V.; Fontecave, M. Biomimetic
assembly and activation of [FeFe]-hydrogenases. Nature 2013, 499,
66−69.
(47) Izawa, T.; Terao, Y.; Suzuki, K. Syntheses of optically active γ-
ketothiols and the esters by lipase-catalyzed hydrolysis via α-
acetylthiomethylation of ketones. Tetrahedron: Asymmetry 1997, 8,
2645−2648.
substituted diiron azadithiolates relevant to the active site of Fe-only
hydrogenases. J. Inorg. Biochem. 2007, 101, 506−513.
(64) Kilgore, U. J.; Roberts, J. A. S.; Pool, D. H.; Appel, A. M.;
Stewart, M. P.; DuBois, M. R.; Dougherty, W. G.; Kassel, W. S.;
Bullock, R. M.; DuBois, D. L. [Ni(PPh2NC6H4X2)2]2+ Complexes as
Electrocatalysts for H2 Production: Effect of Substituents, Acids, and
Water on Catalytic Rates. J. Am. Chem. Soc. 2011, 133, 5861−5872.
(65) Felton, G. A. N.; Mebi, C. A.; Petro, B. J.; Vannucci, A. K.;
Evans, D. H.; Glass, R. S.; Lichtenberger, D. L. Review of
electrochemical studies of complexes containing the Fe2S2 core
characteristic of [FeFe]-Hydrogenase including catalysis by these
complexes of the reduction of acids to form dihydrogen. J. Organomet.
Chem. 2009, 694, 2681−2699.
̈
̈
(66) Weber, K.; Kramer, T.; Shafaat, H. S.; Weyhermuller, T.; Bill,
E.; van Gastel, M.; Neese, F.; Lubitz, W. A Functional [NiFe]-
Hydrogenase Model Compound That Undergoes Biologically
Relevant Reversible Thiolate Protonation. J. Am. Chem. Soc. 2012,
134, 20745−20755.
(48) Angamuthu, R.; Chen, C.-S.; Cochrane, T. R.; Gray, D. L.;
Schilter, D.; Ulloa, O. A.; Rauchfuss, T. B. N-Substituted Derivatives
of the Azadithiolate Cofactor from the [FeFe] Hydrogenases: Stability
and Complexation. Inorg. Chem. 2015, 54, 5717−5724.
(49) Salzer, A.; Werner, H. A New Route to Triple-Decker Sandwich
Compounds. Angew. Chem., Int. Ed. Engl. 1972, 11, 930−932.
(67) Song, L.-C.; Cao, M.; Wang, Y.-X. Novel reactions of
homodinuclear Ni2 complexes [Ni(RNPyS4)]2 with Fe3(CO)12 to
give heterotrinuclear NiFe2 and mononuclear Fe complexes relevant
to [NiFe]- and [Fe]-hydrogenases. Dalton Trans. 2015, 44, 6797−
6808.
(68) Bomfim, J. A. S.; de Souza, F. P.; Filgueiras, C. A. L.; de Sousa,
A. G.; Gambardella, M. T. P. Diphosphine complexes of nickel:
analogies in molecular structures and variety in crystalline arrange-
ment. Polyhedron 2003, 22, 1567−1573.
(69) CrystalClear and Crystal Structure; Rigaku and Rigaku Americas:
The Woodlands, TX, 2007.
́
́
(50) Cordero, B.; Gomerz, V.; Platero-Prats, A. E.; Reves, M.;
́
Echeverría, J.; Cremades, E.; Barragan, F.; Alvarez, S. Covalent radii
revisited. Dalton Trans. 2008, 2832−2838.
(51) Redin, K.; Wilson, A. D.; Newell, R.; DuBois, M. R.; DuBois, D.
L. Studies of Structural Effects on the Half-Wave Potentials of
Mononuclear and Dinuclear Nickel(II) Diphosphine/Dithiolate
Complexes. Inorg. Chem. 2007, 46, 1268−1276.
(52) Goh, Y. X. C.; Tang, H. M.; Loke, W. L. J.; Fan, W. Y.
Bis(cyclopentadienyl)nickel(II) μ-Thiolato Complexes as Proton
Reduction Electrocatalysts. Inorg. Chem. 2019, 58, 12178−12183.
(53) Bhandari, A.; Maji, R. C.; Mishra, S.; Kumar, A.; Barman, S. K.;
Das, P. P.; Ghiassi, K. B.; Olmstead, M. M.; Patra, A. K. Model
Complexes for the Nip Site of Acetyl Coenzyme A Synthase/Carbon
Monoxide (CO) Dehydrogenase: Structure, Electrochemistry, and
CO Reactivity. Inorg. Chem. 2018, 57, 13713−13727.
(54) Luo, S.; Siegler, M. A.; Bouwman, E. Dinuclear Nickel
Complexes of Thiolate-Functionalized Carbene Ligands and Their
Electrochemical Properties. Organometallics 2018, 37, 740−747.
(55) Yao, S. A.; Martin-Diaconescu, V.; Infante, I.; Lancaster, K. M.;
(70) (a) Sheldrick, G. M. SHELXS97, A Program for Crystal Structure
̈
̈
Solution; University of Gottingen: Gottingen, Germany, 1997.
(b) Sheldrick, G. M. A short history of SHELX. Acta Crystallogr.,
Sect. A: Found. Crystallogr. 2008, 64, 112−122.
(71) Sheldrick, G. M. SHELXT-Integrated space-group and crystal-
structure determination. Acta Crystallogr., Sect. A: Found. Adv. 2015,
71, 3−8.
̈
Gotz, A. W.; DeBeer, S.; Berry, J. F. Electronic Structure of Ni2E2
Complexes (E = S, Se, Te) and a Global Analysis of M2E2
n‑
Compounds: A Case for Quantized E2 Oxidation Levels with n =
2, 3, or 4. J. Am. Chem. Soc. 2015, 137, 4993−5011.
(56) Eberhardt, N. A.; Guan, H. Nickel Hydride Complexes. Chem.
Rev. 2016, 116, 8373−8426.
(57) Song, L.-C.; Wang, Y.-X.; Xing, X.-K.; Ding, S.-D.; Zhang, L.-
D.; Wang, X.-Y.; Zhang, H.-T. Hydrophilic Quaternary Ammonium-
Group-Containing [FeFe]-Hydrogenase Models: Synthesis, Struc-
tures, and Electrocatalytic Hydrogen Production. Chem. - Eur. J. 2016,
22, 16304−16314.
(58) Bard, A. J.; Faulkner, L. R. Electrochemical Methods:
Fundamentals and Applications, 2nd ed.; Wiley: Hoboken, NJ, 2001.
(59) Felton, G. A. N.; Glass, R. S.; Lichtenberger, D. L.; Evans, D. H.
Iron-Only Hydrogenase Mimics. Thermodynamic Aspects of the Use
of Electrochemistry to Evaluate Catalytic Efficiency for Hydrogen
Generation. Inorg. Chem. 2006, 45, 9181−9184.
(60) Rountree, E. S.; McCarthy, B. D.; Eisenhart, T. T.; Dempsey, J.
L. Evaluation of Homogeneous Electrocatalysts by Cyclic Voltamme-
try. Inorg. Chem. 2014, 53, 9983−10002.
(61) Borg, S. J.; Behrsing, T.; Best, S. P.; Razavet, M.; Liu, X.;
Pickett, C. J. Electron Transfer at a Dithiolate-Bridged Diiron
Assembly: Electrocatalytic Hydrogen Evolution. J. Am. Chem. Soc.
2004, 126, 16988−16999.
(62) Song, L.-C.; Han, X.-F.; Chen, W.; Li, J.-P.; Wang, X.-Y.
Dithiolato- and halogenido-bridged nickel-iron complexes related to
the active site of [NiFe]-H2 ases: preparation, structures, and
electrocatalytic H2 production. Dalton Trans. 2017, 46, 10003−
10013.
(63) Dong, W.; Wang, M.; Liu, T.; Liu, X.; Jin, K.; Sun, L.
Preparation, structures and electrochemical property of phosphine
I
https://dx.doi.org/10.1021/acs.organomet.0c00130
Organometallics XXXX, XXX, XXX−XXX